What's a 'window'?

[norb]

...seems like a daft question. But Regs designate a window to the outside a 'controlled fitting' so its kind of important. I have a floor to ceiling (almost) aperture which has a window in the top half and a cosmetic panel in the bottom half. The panel is hardwood. Is my 'window' just the top half or does the bottom half also amount to a 'window'. I definitely can't see through the bottom half! If its not a 'window' I guess it must be a 'wall'.
On reading Part 'L' (well some of it) such a design would no longer be permitted as the bottom half is more or less a heat sink. I'm a bit surprised it would have been permitted seven years ago when the building conversion was done. Anyway I plan to box out the interior and add insulation and window board to (vastly) improve insulation but in the absence of an external brick member even then the insulation will be less than desirable.

 

[^woody^]

Something that is not a door.

 

[foxhole]

window is usually only the section that’s glazed .

 

[freddiemercurystwin]

window is usually only the section that’s glazed .

A window can can have a blank panel and still be a window, it's called a spandrel panel.

 

[clifford1]

You can have a window in a door, you can have a window that is a door, you can have a door in a window. You can have an arrow slit in a castle that is neither a door nor a window.
Before I converted it, our kitchen was the old dairy, and it didn't have any glazed windows, just holes with wooden shutters that opened for light and ventilation. It was meant to be cold, and was!

 

[norb]

Thanks all for your observations. Without leading them, and providing a photo, Building Control treated the lower panel as a wall - a 'thermal element' - but due to its size in proportion to the whole wall, it is outside part 'L' requirements for a 'thermal renovation' and Building Control application.
Regardless, it will be much, much warmer once I have added a couple of layers of insulation behind the panel.